Control apparatus for tandem rolling mills



Jan. 30, 1968 TosHlAKl MAEKAWA ETAL.. 3,365,920

CONTROL APPARATUS FOR TANDEM ROLLING MILLS Filed Aug. 28, 1964 ROY/mg speed V ma. Loano ATTORNEY United States Patent G 3,365,920 CONTROL APPARATUS FOR TANDEM ROLLING MILLS Toshiaki Maekawa and Shigeyoshi Kawano, Hitachi-shi,

Japan, assignors to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Ang. 28, 1964, Ser. No. 392,686 Claims priority, application Japan, Sept. 2, 1963, Sil/46,302 6 Claims. (Cl. 72-10) This invention relates to tandem rolling mills and more particularly to control apparatus therefore for compensating any variation in the work. gap between rolls which takes place during the step of increasing or decreasing the rolling speed of rolls for thereby maintaining the properly established work gap at all times.

ln common rolling mills, the Work gap between rolls, that is, an amount of stroke of rolls relative to each other varies with relation to rolling speed of rolls. This is because thickness of oil films in the back-up roll bearings varies With relation to the rotating speed of the back-up rolls. In `a rolling mill or a tandem mill, each roll stand has its individual rolling speed-work gap characteristic, and the work gap between rolls is generally narrowed as the rolling speed gets higher. it is therefore possible to compensate the work gap for variation relative to the speed of tandem rolling mills, taking advantage of the above-mentioned rolling speed-work gap characteristic individual to each roll stand. Such manner of compensation is disclosed, for example, in the specification of Japanese patent application No. 38198/ 1958 according to which a rolling speed-work gap variation characteristic is ca1- culated beforehand and compensation of the work gap between rolls relative to rolling speed is effected on the basis of the characteristic curve.

The present invention relates to control `apparatus for a tandem rolling mill provided with means for work gap compensation for the rolling speed variation as described above, and has for its primary object t-o provide means for simplifying the establishment of a proper amount of `stroke of rolls relative to each other during the starting step of a tandem rolling mill.

Another kobject of the present invention is to provide means for equalizing the tension between roll stands of a tandem rolling mill during operation.

A further object of the present invention is to provide work gap compensating means which is inexpensive and can easily be affixed to an existing rolling mill without any necessity of reconstructing the same.

As is generally known, it is very difficult to effect proper operation of a tandem rolling mill because speeds of rolls at respective roll stands must be closely controlled in harmonious relation with one another and a close re* lation exists between an amount of relative stroke of rolls in a particular roll stand and a tension between the roll stand and an adjacent roll stand. This difculty is especially marked when the rolling speed is increased or decreased. Therefore, a general practice is to provide work gap control at the rst stage roll stand and toprovide tension control at the last stage roll stand. According to such practice, intermediate roll stands are arranged to operate with individual work gaps and rolling speeds Iset at the beginning of the operation and thereafter are left uncontrolled. A considerably satisfactory performance can be obtained even with such method of control when the rolling speeds are relatively low. However, when the ratio of the rolling speed at the rst stage roll stand to the rolling speed at the last stage roll stand (this speed ratio also relating to the reduction ratio) becomes considerably great, the work gap control at the iirst stage roll stand and the tension control at the last stage roll stand ICC can no longer compensate for the variation of the work gap with relation to rolling speed. This will result in an inaccurate thickness of iinal product and vat the same time great imbalance in the tension between respective roll stands may result in severing of material in the worst case.

Assuming, for example, that a sheet material 3.0 mm.

y thick is rolled to a sheet product 0.3 mm. thick. Then, it

is obvious that the ratio of the speed at the last stage roll stand to the speed at the rst stage roll stand is of the order of ten. Assuming `further that the rolling speed at the last stage rolls is 3000 ft./min. Then, the influence of oil tilms at the last stage rolls may be of the order of 0x2 mm., while it may be of the order of 0.1 mm. at the first stage rolls. lt will therefore be seen that the work gap between the rst stage rolls `at the maximum speed is 3.3% less than that during stoppage and the work gap in the case of the last stage rolls at the maximum speed is in fact 66.7% less than that during stoppage. Thus, the rate of thickness reduction in the outgoing product becomes greater than that of the incoming material and a great difference is developed between volumes of the incoming and outgoing material, resulting in unbalance of tension between the roll stands. The nal product sheet fed out of the last stage rolls will have an extremely small thickness or will be extremely thinner than the standard thickness.

However, in practical operations, such detrimental result hardly takes place because the operators incessantly compensate the work gap between rolls at each roll stand. For the sake of proper compensation, the operators must be skilled in the operation and must have an extremely high technical skill. Due to the fact that thickness control in a tandem rolling mill is associated with many factors and due to a recent trend towards a high rolling speed, it is no longer possible to completely control the rolling operation by manual means. Even if it is possible, an eX- cessively long time will be required to establish a proper amount of roll gap for each of roll stands and material as well as electric power will be Wastefully consumed.

Therefore, a further object of the present invention is to provide effective control apparatus which can completely compensate for any variation of the work gap depending on the rolling speed of a tandem rolling mill whereby to reduce the time required for setting a proper amount of roll gap at the beginning of operation of the rolling mill as well as the time required for the rolling mill t-o reach the normal steady speed after the rolling mill has been placed in operation to thereby effect economical operation of the rolling mill.

According to the present invention, there is provided a control apparatus for a tandem rolling mill comprising a plurality of control units disposed independently of one another on at least a last stage roll stand and roll stands in the vicinity thereof, each of said control units comprising speed detecting means for detecting the rolling speed, work gap compensation means operative in response to the detected rolling speed for generating a work gap compensation signal, and auxiliary depressing means -operative in response to the work gap compensation signal to maintain the properly established work gap between rolls.

According to the present invention, there is also provided a control apparatus fora tandem rolling mill comprising a plurality of control units disposed independently p of one another on all of roll stands, each of said control units comprising speed detecting means for detecting the rolling speed, work gap compensation means operative in response to the detected rolling speed for generating a work gap compensation signal, and auxiliary depressing means operative in response to the work gap compensation signal to maintain the properly established work gap between rolls.

There are other objects and particularities of the present invention which will become obvious from the following description with reference to` the accompanying drawings, in which:

FIG. l is a diagrammatic arrangement of a control apparatus embodying the present invention;

FIG. 2 is a diagrammatic arrangement showing detail of parts ofthe apparatus in FIG. l; and

FIG. 3 is a graphic representation of the rolling speedwork gap characteristic forming the basic principle of operation of the apparatus of the present invention.

First referring to FIG. l, there is shown a tandem rolling mill to which the present invention is applied. Although the rolling mill is shown as having four stages A, B, C and D, the invention is also applicable to any other tandem mills having a different number of stages. According to FIG. l, the control apparatus of the invention has four control units each disposed on one roll stand. Each control unit comprises a speed detecting means PG for detecting the rate of rotation of rolls 1 and 2, a work gap compensation means FG responsive to an output from the detecting means PG to generate a predetermined work gap compensation signal and an auxiliary depressing means BSD operative in response to the work gap compensation signal from the work gap compensation means FG. Symbols X1 and X3 designate thickness -gauges disposed at the first stage roll stand A and the last stage roll stand D, respectively. The thickness gauges X1 and X3 are arranged to supply their output to respective main depressing means MSD, thus forming an automatic thickness control system.

Now, one of such control units will be described in more detail with reference to FIG. 2. The working rolls 1 and 2 are driven by an electric motor 10 to roll a workpiece S. The working rolls 1 and 2 are backed up by backeup rolls 3 and 4, respectively. A depressing screw 5 is arranged to be driven by a main depressing motor 7 through a differential -gear 6 to provide a required amount of stroke to the roll 1 relative to the roll 2, that is, to establish a required work gap between the rolls 1 and 2. Arrow 8 designates a main depressing signal applied to the main depressing motor 7. The above arrangement is almost similar to a conventional arrangement.

According to the present invention, a speed detecting means 11 is operatively connected with the electric motor for measuring the rolling speed v and supplying it into a function -generator 12 as a variable. The function generator 12 is so adjusted that it has an operational characteristic which is entirely the same with a relation between work gap variation due to oil films and the rolling speed. The relation between the rolling speed v and the work gap variation d or an amount of work gap compensation has a characteristic as shown by a characteristic curve in FIG. 3. From the curve it will be seen that the amount of work gap compensation d is substantially pro portional to the rolling speed v, that is, the Work gap is inversely proportional to the rolling speed v. The function generator 12 sends out a compensation signal which is supplied to a control means 13 for controlling an auxiliary depressing motor 14. The auxiliary depressing motor 14 drives the depressing screw 5 through the differential gear 6 to effect the required compensation. An amount of rotation of the auxiliary depressing motor 14 is transmitted through a gear 2t), a selsyn transmitter 21, a selsyn receiver 22, and a reduction gear 23 to a function generator 24 which consists of a rheostat 30 and a power source 31. Output from the function generator 24 is fed back into the control means 13. Since work gap variation due to thickness variation of oil films is independent of the position of the upper roll 1 relative to the lower roll 2, the upper roll 1 must always be depressed by the work gap compensation mechanism by an amount which is solely determined by the rolling speed. In the embodiment 4 shown in FIG. 2, the work gap compensation mechanism is provided entirely independently of the main depressing mechanism and mechanical outputs of both of the mechanisms are compounded with each other by means of the differential gear 6. However, it will easily be understood that electrical compounding instead of mechanical compounding may be employed to drive the depressing motor, and in such a case, only one depressing motor will suffice.

In operation, as the rolling speed is increased, the work gap between rolls is reduced. The increased rolling speed is detected by the speed detecting means 11 and the function generator 12. operates in response to the detected speed to gene-rate a compensation signal. This signal is supplied to the control means 13, and the auxiliary depressing motor 14 is thereby driven and acts to widen the work gap between the rolls through the differential gear 6. It will be obvious that oil films hardly affect the operation since the function generator has the operating characteristic which is entirely the same with the rolling speed-work gap variation characteristic. No further explanation with regard to a case of speed reduction will be necessary because the manner of operation is entire similar to the case of speed increase. According to the invention, very precise compensation can be eected because the amount of rotation of the auxiliary depressing motor 14 is fed back through the gear 20, the selsyn transmitter 21, the selsyn receiver 22 and the function generator 24. Although, in the embodiment shown in FIG. l, the control unit is disposed on each of the roll stands, it will be understood that the effect of the present invention can almost equally effectively -be attained by disposing the control units solely on those roll stands which a-re located in the vicinity of the last stage roll stand where the rate of work gap variation is highest.

From the foregoing description, it will lbe appreciated that mere provision of the control apparatus of simple structure of the invention on an existing rolling mill can completely compensates for the influence of oil films. This is highly advantageous for a tandem rolling mill in which thin metal sheets are rolled at a relatively high speed. In other words, a metal sheet of predetermined thickness can continuously be manufactured even during the step of increasing or ydecreasing the rolling speed, and this ease of thickness maintenance provides a great technical as well as economical advantage.

What is claimed is:

1. A control apparatus for a tandem rolling mill having a plurality of roll stands with working rolls, back-up rolls and main depressing means, comprisng: a plurality of control units respectively disposed independently of one another on at least the last stage roll stand and roll stands in the vicinity thereof; each of said control units comprising speed detecting means for producing signals in accordance with the rolling speed, oil film compensation means operative in response to the speed signal from said speed detecting means for generating an oil film compensation signal in accordance with a predetermined functional relationship, and auxiliary depressing means operative in response to said oil film compensation signal for effecting work gap adjustments independently of the main depressing means.

2. A control apparatus as claimed in claim 1, in which said control units are disposed independently of one another on all of the Iroll stands.

3. A tandem rolling mill, comprising: a plurality of roll stands, each having working rolls, back-up rolls, main depressing means for adjusting the gap between said working rolls, and control means compensating for the oil film thickness between said rolls being responsive solely to the rolling speed and independent of the gap between said working rolls; said control means including speed detecting means for producing speed signals solely in accordance with the rolling speed of said rolls, oil lm compensation means responsive solely to said speed signals from said speed detecting means for generating an oil film compensation signal in accordance with a predetermined functional relationship, and auxiliary depressing means operative solely in response to said oil film compensation signal for eiecting work gap adjustments independently of said main depressing means.

4. The device of claim 3, wherein each of the roll stands of said rolling mill includes one of said control means.

5. The device of claim 4, including a differential gear means driven by said main depressing means and said auxiliary depressing means for relatively moving said rolls.

6. The device of claim 3, including a differential gear UNITED STATES PATENTS 2,851,911 9/1958 Hassenberg 72-8 3,081,652 3/1963 Wright 72--8 3,081,653 3/1963 Kincaid 72-8 3,158,049 11/1964 Huntley 72-8 RCHARD J. HERBST, Primary Examiner.

K. C. DECKER, Assistant Examiner. 

1. A CONTROL APPARATUS FOR A TANDEM ROLLING MILL HAVING A PLURALITY OF ROLL STANDS WITH WORKING ROLLS, BACK-UP ROLLS AND MAIN DEPRESSING MEANS, COMPRISING: A PLURALITY OF CONTROL UNITS RESPECTIVELY DISPOSED INDEPENDENTLY OF ONE ANOTHER ON AT LEAST THE LAST STAGE ROLL STAND AND ROLL STANDS IN THE VICINITY THEREOF; EACH OF SAID CONTROL UNITS COMPRISING SPEED DETECTING MEANS FOR PRODUCING SIGNALS IN ACCORDANCE WITH THE ROLLING SPEED, OIL FILM COMPENSATION MEANS OPERATIVE IN REPONSE TO THE SPEED SIGNAL FROM SAID SPEED DETECTING MEANS FOR GENERATING AN OIL FILM COMPENSATION SIGNAL IS ACCORDANCE WITH A PREDETERMINED FUNCTIONAL RELATIONSHIP, AND AUXILIARY DEPRESSING MEANS OPERATIVE IN RESPONSE TO SAID OIL FILM COMPENSATION SIGNAL FOR EFFECTING WORK GAP ADJUSTMENTS INDEPENDENTLY OF THE MAIN DEPRESSING MEANS. 